Thin film magnetic head having magnetic layers of different thickness and manufacturing method therefor

ABSTRACT

A thin film magnetic head for performing recording and readout operations to a magnetic recording medium and a method of manufacturing the head. The magnetic head .[.comprises.]. .Iadd.includes .Iaddend.a substrate, a first magnetic layer formed on the substrate, a conductor coil on the first layer and a second magnetic layer formed on the conductor coil and the first magnetic layer. The second magnetic layer is imparted with a greater thickness than the first magnetic layer to thereby strengthen the magnetic field for recording and reducing the peak shift making appearance in readout operation due to interference between successively read-out waveforms. The thin film magnetic head exhibits an improved reproduction characteristic which permits reproduction with high fidelity the magnetized locations recorded on the medium with high recording density which assures an improved recording characteristic. .Iadd.By controlling the thickness of the second magnetic layer at an inclined portion thereof, magnetic saturation thereat is substantially prevented. .Iaddend.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film magnetic head which can befabricated with the aid of thin film forming means for forming thinfilms through plating, vapor deposition, sputtering or the like and ahigh precision pattern forming means referred to as photolithography.

2. Description of the Prior Art

The magnetic head whose magnetic circuit is implemented with the aid ofthe thin film technology is generally considered advantageous in thatthe recording density can be enhanced and increasingly tends to replacethe magnetic head of the type in which a coil is wound on a ferrite orpermalloy piece. A typical structure of such thin film head is describedin detail in Japanese Patent Application Laid-Open No. 84020/80 whichcorresponds to U.S. Pat. No. 4,219,854. For attaining an increased datarecording density with the magnetic circuit of the thin film magnetichead, it is a fundamentally important factor to reduce the thickness ofa magnetic layer exposed on an air bearing surface and hence thethickness of a pole piece of the magnetic head. However, in case one andthe same magnetic head is destined to serve for both recording andreading data on and from a recording medium, thinning of the pole pieceas described above can never be the necessary and sufficient conditionfor attaining the increased recording density. More specifically, uponrecording operation, it is necessary to excite the magnetic circuit bycausing an exciting current to flow through the conductor coil tothereby generate a desired magnetic field in the recording medium whichis disposed with a predetermined gap from the air bearing surface of themagnetic head. In this connection, the magnetic layer of a reducedthickness is readily magnetically saturated and therefore an increasedexciting current can not produce the effective magnetic field. Under thecircumstances, it is important to determine the range of the thicknessof the magnetic layer which satisfies the conditions for assuring boththe recording and the reading operations in a satisfactory manner. Atpresent, however, the prevailing trend is toward the imparting of a highcoercive force to the recording medium in an effort to attain the highrecording density, which means that the magnetic head has to be capableof producing a magnetic field of a correspondingly increased strength.To meet this requirement, the range of the thickness of the magneticlayer in which both the recording and the reading operations can beeffected satisfactorily is inevitably significantly narrowed and, in aextreme case, such thickness range will become actually no moreavailable, giving rise to a serious problem to be dealt with.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a thin film magnetichead which is capable of realizing an increased density recording byproducing a magnetic field of a sufficient strength for the satisfactoryrecording.

It is another object of the present invention to provide a method ofmanufacturing the thin film magnetic head mentioned above.

.Iadd.It is a further object of the present invention to provide a thinfilm magnetic head having magnetic layers for preventing magneticsaturation and a manufacturing method therefor. .Iaddend.

The present invention starts from the discovery that a magnetic circuitconstituted by a first magnetic layer of a given thickness and a secondmagnetic layer of a greater thickness than that of the first magneticlayer is capable of strengthening more the magnetic field for therecording and at the same time more effective for reducing a phenomenonof so-called peak shift, which a high density recording entails, broughtabout due to interference between subsequent readout waveforms, ascompared with the magnetic circuit constituted by the first and thesecond magnetic layers of a same thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an isolated or discrete waveform produced bya magnetic head upon reading operation.

FIG. 2 is a schematic sectional view of a hitherto known thin film head.

FIG. 3 is a view to illustrate the principle of the invention and showssynthesization of discrete waveforms read out successively by a thinfilm magnetic head upon reading operation.

FIG. 4 is a view for illustrating the principle of the invention andgraphically shows relationship between the thickness of a pole piece andthe peak shift.

FIG. 5 is a sectional view of a thin film magnetic head according to anembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the invention will be described in more detail by referring to thedrawings.

FIG. 1 shows an isolated or discrete waveform which corresponds to asingle magnetic transition on a recording medium read out by a thin filmmagnetic head. It will be seen from this figure that undershoots areproduced at both sides of the discrete waveform. Such appearance of theundershoots is ascribable to the fact that the thickness of a magneticlayer exposed on an air bearing surface of the thin film magnetic, headand hence the thickness of the pole piece are on the order of severalmicrons, in contrast to the bulk magnetic head of the past. Whenobserved carefully, it will further be seen that the undershoots differin magnitude from each other. More specifically, the undershoot producedat the lefthand side of the read out waveform relative to the peakposition thereof is different in magnitude from the undershoot producedat the righthand side. This can be explained by such a common structureof the conventional thin film magnetic head in which a first magneticlayer 1 extends perpendicularly to a plane of a recording medium 3 whilesecond magnetic layer 2 is bent at an intermediate portion 4, asschematically shown in a sectional view of FIG. 2. In the isolatedreadout waveform, the undershoot of smaller magnitude corresponds to thesecond magnetic layer, while the undershoot of greater magnitudecorresponds to the first magnetic layer. Now, it will be examined whatinfluences the difference in magnitude of the undershoots exerts to thehigh density recording. It is generally accepted that the waveformsresulting from data recorded at a high density can be synthesized withconsiderably high precision by superposing the discrete or isolatedwaveforms one another. Let's assume that a given magnetic transition isfollowed by a succeeding magnetic transition with an extremely shortinterval therebetween. The readout waveforms corresponding to these twomagnetic transitions can be obtained as a waveform shown in FIG. 3 at(c) by superposing the isolated or discrete waveforms shown in FIG. 3 at(a) and (b) to each other. It will be noted that the positions of thepeaks of the synthesized waveform are shifted from the correspondingpeaks of the discrete waveforms, as indicated by ΔT₁ and ΔT₂ in FIG. 3at (c). In other words, the so-called peak shift has occurred in thesuperposed or synthesized waveform. The magnitude of the peak shiftdetermined by the steepness of the slope of a foot or base portion ofone discrete waveform lying at the position corresponding to the peak ofthe other waveform. It will be readily understood that when the positionof the peak of the succeeding discrete waveform lies in the vicinity ofthe position which corresponds to the zero-crossing of the precedingdiscrete waveform, the above mentioned slope of the preceding waveformat that position depends on that magnitude of the correspondingundershoot. Accordingly, comparison of the peak shifts ΔT₁ and ΔT₂ witheach other will result in that that magnitude of the peak shift ΔT₁corresponding to the smaller undershoot is smaller than that of the peakshift ΔT₂. FIG. 4 graphically illustrates experimentally establishedrelationships between the peak shifts ΔT₁ and ΔT₂ and the thickness ofthe pole piece of a thin film magnetic head with the latter beingselected as a variable. As will be appreciated from this graph, themagnitude of the phase shift ΔT₂ is greater than that of the phase shiftΔT₁ and exhibits a greater tendency to depend on the film thickness thanthat of the phase shift ΔT₁ does for a given thickness of the polepiece. Thus, it can be said that the thickness of the first magneticlayer should be decreased in order to reduce effectively the peak shiftin question. More specifically, only the first magnetic layer shouldrather be thinned than both the first and the second magnetic films bedecreased in thickness by a same ratio.

On the other hand, in the recording operation, it is required to producea magnetic field of high strength on the air bearing surface of themagnetic head in order to magnetize the recording medium, as describedhereinbefore, while the magnetic circuit should be realized in such astructure that magnetic saturation is prevented from occurring in themagnetic path as far as practicable. To this end, it is important toincrease not only the saturation magnetic flux density of the magneticlayer which constitutes the magnetic path but also the cross-sectionalarea of the magnetic path. When the thin film magnetic head shown inFIG. 2 is examined in respect to the structure of the magnetic path inthe light of the viewpoint mentioned above, it is seen that the bent orsloping portion 4 of the second magnetic layer presents a problem. Ingeneral, when a thin film is formed on a horizontally laid member havinga step thereon through vapor deposition, sputtering, plating or the likeprocess from above, the thickness of the film formed on a slantedportion or edge of the step is smaller than that of the film formed onthe horizontal portion thereof. This tendency is remarkable particularlyin the film formation through the vapor deposition and the sputtering.The relative ratio of film thickness between the horizontally laidportions and the slanted portion (this ratio is referred to as coveragefactor) depends on the angle of inclination of the slanted portion andgenerally ranges from 0.7 to 0.8 for the inclination angle of about 30°.It can thus be said that the magnetic saturation is most likely to occurat the slanted portion which is smallest in respect of thecross-sectional area in the whole structure of the thin film magnetichead. Accordingly, in order to make use of the second magnetic layerunder magnetically the same condition as the first magnetic layer, thethickness of the second magnetic layer should preferably be selected.Iadd.to be a predetermined thickness .Iaddend.at a value equal to thequotient obtained by dividing the thickness of the first magnetic layerby the coverage factor. In other words, the thickness of the secondmagnetic layer should be .Iadd.about .Iaddend.1.2 to 1.4 times as greatas that of the first magnetic layer. In the foregoing, the reason whythe thickness of the second magnetic layer should be increased in bothcases of recording and reading as compared with that of the firstmagnetic layer, has been explained from the view point of resultantadvantageous effect.

in the following, an embodiment of the thin film magnetic head accordingto the present invention will be described by referring to FIG. 5 whichshows in a schematic sectional view a thin film magnetic head for amagnetic tape equipment. The first magnetic layer denoted by a referencenumeral 11 is formed through sputtering on a substrate 10 in apredetermined pattern in thickness of 1.5 μm and is substantiallyplanar. .Iadd.The first magnetic layer is then overlaid on or arrangedto be overlaying the substrate 10. .Iaddend.The substrate 10 is made ofa single crystal sapphire which exhibits an excellent anti-abrasionproperty. Subsequently, an alumina layer 12 which constitutes atransducing gap is formed to a thickness of 0.5 μm on the first magneticlayer 11, which is followed by formation of a conductor coil 13 in aplanar vortex-like pattern through vapor deposition .Iadd.so that theconductor coil 13 is overlaid on the magnetic layer 11.Iaddend.. Afteran insulation layer 14 of an appropriate material has been formed so asto level the layer of conductor coil 13, the second magnetic layerdenoted by 15 is formed through sputtering in thickness of 2 μm in apredetermined pattern to cover .Iadd.or overlay .Iaddend.the conductorcoil 13 .[.and.]..Iadd., .Iaddend.the insulation layer 14 .Iadd.and thefirst magnetic layer 11.Iaddend.. At that time, the alumina layer isremoved at an end portion on the far side from the air bearing surfaceof the magnetic head so that the first magnetic film 11 and the secondmagnetic film 15 are magnetically shorted at that end portion.Subsequently, terminals (not shown) are formed and finally a protectionlayer 16 of a predetermined thickness is deposited. A plurality of thehead elements thus fabricated are disposed in array are cut at aposition indicated by a dotted broken line in FIG. 5 so that apredetermined gap depth can be attained at the transducing gap definedby the transducing gap alumina layer 12 sandwiched between the firstmagnetic layer 11 and the second magnetic layer 15 at the end indicatedby dotted broken line. The finished magnetic head element is nowobtained. It will be noted that the thickness of the second magneticlayer 15 is selected to be .Iadd.a predetermined thickness of .Iaddend.2μm in contrast to the first magnetic layer which is 1.5 μm thick. Thisis because the coverage factor of the magnetic layer formed throughsputtering on the slanted portions is 0.75. This is, 1.5 μm÷0.75=2 μm.With the aid of the magnetic head element thus realized, two magnetictransitions were recorded with an interval of 2.1 μm on a magnetic tapehaving a coercive force of 600 Oe. The distance between the readoutmagnetic transitions was 2.25 μm. In contrast, in the case of a magnetichead fabricated in the same manner as described above and having howeverthe first and the second magnetic layers both of 2 μm thick, thedistance between the readout magnetic transitions was 2.8 μm. On theother hand, in the case of a magnetic head in which the first and thesecond magnetic layers are both 1.5 μm thick, the corresponding distancebetween the readout transitions was about 2.1 μm. However, it has beenfound that the output level of the last mentioned head is very low. Thiscan be explained by the fact that saturation occurs in the magnetic pathat the time of recording, resulting in that the magnetic transitions arenot recorded on the magnetic tape with adequate magnetization. Theexperimental results mentioned above show obviously that the structureof the thin film magnetic head in which the first and the secondmagnetic layers are realized in different thickness according to theteaching of the invention exhibits the improved characteristicsdesirable for this type of magnetic head to an advantage over the priorart magnetic head.

It should be noted that the difference of 0.5 μm in thickness betweenthe first and the second magnetic layers lies outside the range oftolerance (usually ±10% of the film thickness) to be taken into accountin the formation of these magnetic layers. By the way, there has beenknown a thin film magnetic head of such a magnetic circuit configurationin which inner portions of the magnetic layers are partially thickenedas compared with the thickness of the portions exposed on the airbearing surface of the magnetic head (i.e. the thickness of the polepiece) with a view to improving the recording and reading behavior ofthe head. It will be readily appreciated that the principle of thepresent invention can be equally applied to the thin film magnetic headof such structure, although elucidation is omitted herein.

The present invention has now provided a thin film magnetic head whichcan enjoy the improved readout or reproduction characteristic whichassures the high fidelity reproduction or readout of magnetizedlocations recorded on the medium at an increased recording density,while enjoying simultaneously the improved recording characteristic.Further, the thin film magnetic head according to the invention can bemanufactured through the same process as adopted heretofore without anynoticeable modifications except for only the thickness control of themagnetic layers, which involves no increase in the manufacturing cost.Further, the thin film magnetic head is not restricted in itsapplication to the magnetic tape drive but can be widely used for discdrive or floppy disc drive, and additionally in VTR, PCM audio systemsor the like.

What is claimed:
 1. A thin film magnetic head for performing recordingand reading operations to a magnetic recording medium, comprising asubstrate, a substantially planar first magnetic layer formed on saidsubstrate and having one end facing toward said recording medium, aconductor coil formed above said first magnetic layer, and a secondmagnetic layer formed over said conductor coil and said first magneticlayer, said second magnetic layer being spaced from said first magneticlayer to define a magnetic gap at one end facing toward said recordingmedium and being magnetically shorted to said first magnetic layer at another end opposite to said one end, said second magnetic layer having afirst side portion facing toward said recording medium and a second sideportion opposite to said first side portion, both of said first andsecond side portions being constituted by inclined portions, and saidsecond magnetic layer at least at said one end positioned in oppositionto said first magnetic layer with the magnetic gap being interposedtherebetween being 1.2 to 1.4 times as thick as said first magneticlayer.
 2. A thin film magnetic head according to claim 1, wherein saidinclined portions of said second magnetic layer have a substantiallysame thickness as that of said first magnetic layer.
 3. A method ofmanufacturing a thin film magnetic head for performing recording andreading operations to a magnetic recording medium, comprising the stepsof forming through thin film technique a substantially planar firstmagnetic layer on a substrate so as to have one end facing toward saidrecording medium, a conductor coil on said first magnetic layer, and asecond magnetic layer on said conductor coil and said first magneticlayer, said second magnetic layer being spaced from said first magneticlayer so as to define a magnetic gap at said one end facing toward saidrecording medium and being magnetically shorted to said first magneticlayer at an other end opposite to said one end, said second magneticlayer having inclined portions at a side facing toward said recordingmedium and at the opposite side at which said second magnetic layer ismagnetically shorted to said first magnetic layer, respectively, andsaid second magnetic layer at least at said one end positioned inopposition to said first magnetic layer with the magnetic gap beinginterposed therebetween being 1.2 to 1.4 time as thick as said firstmagnetic layer.
 4. A method of manufacturing a thin film magnetic headaccording to claim 3, wherein said inclined portions of said secondmagnetic layer have a substantially same thickness as that of said firstmagnetic layer.
 5. A thin film magnetic head for performing recordingand reading operations on a magnetic recording medium, comprising:asubstrate; a substantially planar first magnetic layer formed on saidsubstrate; a transducing gap layer formed on said first magnetic layer;a conductor coil formed on said transducing gap layer; and a secondmagnetic layer formed over said conductor coil with an insulatorinterposed between said conductor coil and said second magnetic layer sothat said second magnetic layer has inclined portions, said secondmagnetic layer having one end where said transducing-gap layer issandwiched between said first and second magnetic layers to constitute atransducing gap at said one end, said second magnetic layer having another end magnetically shorted with said first magnetic layer, and saidsecond magnetic layer having a thickness at said one end of saidposition of said transducing gap of 1.2 to 1.4 times the thickness ofsaid first magnetic layer.
 6. A thin film magnetic head for performingrecording and reproducing operations on a magnetic recording medium,comprising:a substrate; a substantially planar first magnetic layerformed on said substrate; a transducing gap layer formed on said firstmagnetic layer; a conductor coil formed on said transducing gap layer; asecond magnetic layer formed over said conductor coil with an insulatorinterposed between said second magnetic layer and said conductor coil,said second magnetic layer having one end portion at which saidtransducing gap layer is interposed between said first and secondmagnetic layers to constitute a transducing gap at said one end portion,said magnetic layer further including a first inclined portion adjacentto said one end portion and a second inclined portion adjacent to another end portion of said second magnetic layer at which said secondmagnetic layer is magnetically shorted with said first magnetic layer,and said second magnetic layer having a thickness at said one endportion of 1.2 to 1.4 times the thickness of said first magnetic layer.7. A method of manufacturing a thin film magnetic head for performingrecording and reading operations on a magnetic recording medium,comprising the steps of:(a) sputtering a magnetic material on asubstrate to form a substantially planar first magnetic layer; (b)providing a first material on said first magnetic layer so as to form alayer constituting a transducing gap; (c) vapor depositing a conductivematerial on said transducing gap layer to form a conductor coil; (d)providing an insulating material on said conductor coil; .Iadd.and.Iaddend. (e) sputtering a magnetic material so as to form a secondmagnetic layer having one end deposited on said transducing gap layer sothat said transducing gap layer is interposed between said first andsecond magnetic layers to constitute a transducing gap at said one end,.Iadd.an .Iaddend.other end where said second magnetic layer isdeposited on said first magnetic layer so that said second magneticlayer is magnetically shorted with said first magnetic layer, and a partof said second magnetic layer between said one end and said.[.another.]. .Iadd.other .Iaddend.end wherein said second magneticlayer is deposited on a surface of a laminate formed through the stepsof (a) to (d) so that said second magnetic layer has inclined portionsthereat, said second magnetic layer being formed with a thickness atsaid one end at the position of said transducing gap of 1.2 to 1.4 timesthe thickness of said first magnetic layer. .Iadd.
 8. A thin filmmagnetic head for performing recording and reading operations to amagnetic recording medium, comprising:a substrate; a first magneticlayer overlaid on said substrate; a conductor coil overlaid on saidfirst magnetic layer; and a second magnetic layer overlaid on said firstmagnetic layer and on said conductor coil, said second magnetic layerbeing spaced from said first magnetic layer to define a magnetic gap atone end facing toward said magnetic recording medium, said secondmagnetic layer being magnetically shorted to said first magnetic layerat an other end opposite to said one end, said second magnetic layerhaving inclined portions at parts thereof overlaying said conductor coilbetween said one end and said other end, said second magnetic layerhaving a predetermined thickness at least at said one end positioned inopposition to said magnetic recording medium of about 1.2 to about 1.4times the thickness of said first magnetic layer. .Iaddend..Iadd.9. Athin film magnetic head for performing recording and reading operationto a magnetic recording medium, comprising: a substrate; a firstmagnetic layer overlaid on said substrate; a conductor coil overlaid onsaid first magnetic layer; and a second magnetic layer overlaid on saidfirst magnetic layer and on said conductor coil, said second magneticlayer being spaced from said first magnetic layer to define a magneticgap at one end facing toward said magnetic recording medium, said secondmagnetic layer being magnetically shorted to said first magnetic layerat an other end opposite to said one end, said second magnetic layerhaving inclined portions at parts thereof overlaying said conductor coilbetween said one end and said other end, said second magnetic layer atleast at said one end positioned in opposition to said magneticrecording medium having a predetermined thickness greater than that ofsaid first magnetic layer opposite thereto, said predetermined greaterthickness being determined by a coverage factor representing therelative ratio of film thicknesses between planar portions and saidinclined portions of said second magnetic layer. .Iaddend..Iadd.10. Athin film magnetic head for performing recording and reading operationsto a magnetic recording medium, comprising: a substrate; a firstmagnetic layer overlaid on said substrate; a conductor coil overlaid onsaid first magnetic layer; and a second magnetic layer overlaid on saidfirst magnetic layer and on said conductor coils; said second magneticlayer being spaced from said first magnetic layer to define a magneticgap at one end facing toward said magnetic recording medium, said secondmagnetic layer being magnetically shorted to said first magnetic layerat an other end opposite to said one end, said second magnetic layerhaving inclined portions at parts thereof overlaying said conductor coilbetween said one end and said other end, said second magnetic layer atleast at said one end positioned in opposition to said magneticrecording medium having a predetermined greater thickness than that ofsaid first magnetic layer opposite thereto, said predetermined greaterthickness being determined in accordance with the angle of said inclinedportions thereof. .Iaddend.